It includes an authentication string that's uniquely linked with your wallet, and a relay specification that's the relay the wallet uses to toss wallet commands. Once you attach that connect string to your client, the auth string allows the client to access your specific wallet. When you zap someone, it sends a command to your wallet through the relay specified in the connect string. The wallet executes the send transaction, and then closes out the transaction which let's the client know the zap was successful. The client then displays its zap indicator letting the user know their zap was successful.